Metallic sheets such as tin-plated steel sheets and electrolytically chromic acid-treated steel sheets called tin-free steel sheets are used for various metallic cans such as beverage cans, food cans, pail cans, and 18-liter cans. Among these, tin-free steel sheets are manufactured by subjecting steel sheets to an electrolytic treatment in a bath containing hexavalent chrome, and are characterized in that they have excellent resin adhesiveness with a coating material or the like.
In recent years, there has been a tendency for usage of hexavalent chrome to be restricted worldwide due to an increase in concern regarding the environment, and an alternative material to the tin-free steel sheet, which is manufactured by using a hexavalent chrome bath, has been requested. As an alternative material to the tin-free steel sheet which does not use chrome, for example, Patent Literature 1 discloses a steel sheet for containers which is subjected to an electrolytic treatment in a tungstic acid solution. In addition, Patent Literature 2 discloses a surface-treated metallic material in which an inorganic surface treatment layer that contains Zr, O, and F as a main component and substantially does not contain a phosphate ion is formed on a surface thereof.
To date, various metallic cans have been manufactured by forming a coating on a metallic sheet such as a tin-free steel sheet and by forming the resultant coated metallic sheet into a can body. However, in recent years, a method in which a laminated metallic sheet (resin-coated metallic sheet), which is obtained by laminating a metallic sheet with a resin such as a plastic film instead of a coating is formed into a can body, has been frequently used so as to reduce the amount of manufacturing-related waste. In the laminated metallic sheet, it is necessary for the resin and the metallic sheet to tightly adhere to each other. In particular, in a laminated metallic sheet that is used to make a beverage can or a food can, since the neck portion of the can is subjected to drawing and ironing, and after the can has been filled with its contents, the resultant can is subjected to a retort sterilization process, strong resin adhesiveness is required in order for a steel sheet-resin adhesion portion subjected to a high degree of forming not to peel off even in a high-temperature wet environment. As a steel sheet for cans subjected to a high degree of forming, a steel sheet for containers which is excellent in terms of weldability, corrosion resistance and coating material adhesiveness, and furthermore, excellent in terms of film adhesiveness, particularly, film adhesiveness at a highly formed portion (hereinafter, referred to as highly-formed-film adhesiveness) has been required.